It is imperative that new, effective, economical and efficient methods to prevent and manage chronic disease be developed. Non-invasive monitoring of changes in potassium offers an exciting potential strategy. Potassium homeostasis is impaired in patients with cardiovascular and renal disease, particularly in those with advanced age or diabetes. Importantly, potassium changes are often exacerbated by many medications used to treat these disorders. There is emerging and robust evidence that even modest increases or decreases in potassium in patients with cardiovascular or renal disease may increase risk of hospitalization and death. Traditional assessment of potassium values always requires access to blood - either by phlebotomy or other skin puncture. A non-invasive strategy that can be integrated into existing remote monitoring systems will enhance patient safety, comfort and convenience. It is widely accepted that marked increases or decreases in potassium are accompanied by changes in the surface EKG. We have acquired compelling preliminary data showing that even very modest changes in potassium, within the physiologic range, are also accompanied by detectable and quantifiable changes in the surface EKG. This proposal involves validation and refinement of a noninvasive technology that permits determination of potassium values without obtaining blood by tracking the body's EKG responses to potassium levels. This technology will enhance safety and promote independent living by identifying when dialysis schedules should be modified in patients with end stage renal disease and determining when individuals with cardiac disease require intervention for significant alterations in potassium levels. We propose the following concepts: 1) Small but clinically important changes in plasma potassium are accompanied by quantifiable changes in the processed surface ECG; 2) Once an individualized baseline ECG is obtained for a known potassium value, subsequent changes in potassium can be determined noninvasively by measuring changes in the processed ECG; 3) Potassium related ECG changes can be used to track changes in potassium levels in the clinical context. In preliminary data in patients undergoing hemodialysis, we have non-invasively determined potassium levels with an accuracy of up to 95%, and found that analysis can be performed on a single lead, indicating that this approach may ultimately be adapted into a wearable ECG sensor in ambulatory individuals, and integrated into current remote monitoring systems. In this study, we aim first, to adapt and refine our algorithms in an animal model to permit accurate potassium determination through specially processed electrocardiographic signals; second, to demonstrate the accuracy of non-invasively determined potassium values in patients undergoing dialysis, in whom significant dialysis-induced potassium changes are likely to occur; and third, to validate the solution in an ambulatory, outpatient dialysis population.